The invention relates to a method of using an estimator to determining a force, which acts from the outside on a steering gear of a steering device in a vehicle by way of a steering linkage, wherein a motor for generating a steering torque is assigned to the steering device.
The invention further relates to a control device for the control/regulation of a steering device in a vehicle, wherein the steering device comprises a steering linkage, a steering gear and a motor for generating a steering torque, and wherein the control device comprises means for detecting a motor torque of the motor and an estimator for determining a force acting from the outside on the steering gear.
The invention further relates to a computer program which can run on a control device for the control/regulation of a steering device.
In modern steering devices, in particular in an electric power steering system (EPS) or a so-called steer-by-wire (SbW) steering system, a force level is determined which is then present at a steering means, such as a steering wheel, and counteracts the force applied by the driver or amplifies the force applied by the driver in order to provide the driver with a driving feel that corresponds to the actual driving situation and, for example, to report back information about the current roadway conditions by way of the steering wheel. The magnitude of the force is therefore dependent upon the current driving state and, in particular, upon the transversal forces or the resulting forces that act on the steering by way of a steering linkage, e.g. tie rods.
In order to determine the force level, it is known to determine a transversal force on the basis of a lateral acceleration measured using appropriate sensors. It is likewise known to determine the lateral acceleration using a vehicle model on the basis of a current steering angle and a current vehicle speed and, on the basis thereof, to deduce the transversal force. To this end, a suitable vehicle model must be generated for every vehicle in which the lateral acceleration should be determined in this manner, which is, however, very time-consuming and cost-intensive.
A method is described in DE 101 15 018 A1, by way of which the desired force level is calculated and set on the basis of signals within the steering system. To this end, a motor torque is first determined for an electric motor assigned to the steering, which is necessary to permit torque-free steering. This motor torque is then multiplied by a factor which is dependent upon a current vehicle speed and a current manual torque applied by a driver. The result is the desired force level.
Furthermore, it is known from DE 101 15 018 A1 to use disturbance values such as tie rod forces to calculate the desired force level. Although such disturbance values can be measured in principle, measurement technology therefor is not installed in vehicles for reasons of cost. These disturbance values are therefore estimated.